Embryotoxicity may result from a variety of environmental factors including in utero exposure of the fetus to drugs or alcohol. The exact mechanism for teratogenesis is unclear, however, it is plausible that many toxicities arise from the formation of reactive intermediates caused by fetal oxidation of xenobiotics by CYP450 enzymes. Of toxicological significance is the P450 CYP2E1 which bioactivates most of its substrates. The possibility that fetal and adult CYP2E1 catalyze similar substrates and therefore cause toxicities is conceivable. Indeed, conversion of ethanol to its toxic metabolite, acetaldehyde, is mediated by CYP2E1 in human hepatic microsomes from both adult and fetuses 18 weeks gestation or older. Therefore, the goals of this application are to compare and contrast structural characteristics, that may lead to possible alterations in functional characteristics, of human adult and fetal CYP2E1. To accomplish these goals the fetal enzyme will be amplified, cloned, sequenced and expressed in E. coil. The sequence of fetal CYP2E1 will be compared to that of the adult enzyme. Catalytic properties of the expressed recombinant fetal and adult CYP2E1 will be determined and specificity and kinetic parameters compared between the two enzymes. Results from these experiments will provide information regarding the role of ontogeny in regulating CYP2E1 function. Moreover, information may be gained regarding CYP2E1-substrate interactions, which will ultimately provide a means for predicting certain chemical- initiated teratogenesis in humans.